The exterior walls of modern buildings, especially residential type structures, often include a frame, covered on the exterior side with a sheathing material. Wood sheet products, such as CDX plywood or oriented strand board (OSB), are often used as the sheathing material. Finish siding material is applied over the sheathing for weather and physical damage protection and to give the structure a more attractive appearance.
The finish siding used in construction is usually not completely resistant to water and water vapor infiltration. Water from precipitation may migrate or leak through finish siding. Moreover, moisture-laden air may permeate the finish siding layer during periods of warmer outdoor temperature. When the outdoor temperature drops, the moisture may condense from the air as liquid water onto the surfaces of the finish siding and sheathing, even forming ice at lower temperatures. This condensation may penetrate and saturate porous finish siding material or sheathing material.
Water in any form remaining for extended periods within, or on surfaces of, the finish siding or sheathing materials may have deleterious effects for a structure and its inhabitants. Porous materials may undergo temporary or permanent dimensional changes from water infiltration, including warping and swelling, and subsequent shrinking as the material dries. These dimensional changes can loosen connections between building components, and open seams or cracks, leading to more water infiltration. Organic materials, such as sheathing made from wood products, may rot or become a location for mold and mildew growth. Rotting or other such deterioration may compromise the structural integrity of the building. In addition, mold or mold spores may penetrate into the interior of the structure, causing adverse health consequents for occupants.
One or more layers of building paper are typically applied over sheathing material to retard water infiltration. Usually, this building paper is asphalt impregnated felt material or spun-bonded polyolefin sheeting. Asphalt felt material may become saturated with water if exposed to moisture over a long period, however, in turn causing moisture in the sheathing. The polyolefin materials, on the other hand, are designed to pass moisture vapor, while preventing the passage of bulk water. Without the circulation of dryer air, however, any condensed water present between the polyolefin material and the sheathing may not dry out and the sheathing is consequently exposed to moisture over a long period.
An air space is sometimes created between the finish siding and the building paper covered sheathing material in order to provide a space for air circulation. Typically, an air space is created by first affixing furring strips made from solid material to the sheathing and then affixing the siding to the furring strips. One or more openings to the exterior are provided leading to the space to permit air circulation. Drier air from the exterior circulating within this space may evaporate and absorb any bulk moisture present on the surfaces of the building paper, sheathing, or finish siding.
It is, however, necessary that ventilation air freely circulate into this air space in order that a continuous supply of dry air is available to replace the moisture-laden air resulting from the evaporation process. Due to the very confined nature of this air space, and the need to provide a continuous finish siding layer to minimize water leakage to the extent possible, adequate ventilation of this space has proven to be difficult to achieve. For instance, the solid furring strips themselves may block or restrict air circulation.
What is needed is an apparatus, system, and method for effectively ventilating a space provided in the wall system of a structure that overcomes the aforementioned problems.